Nonaqueous electrolytes and nonaqueous-electrolyte secondary batteries employing the same

1. A nonaqueous electrolyte mainly comprising a nonaqueous solvent and an electrolyte dissolved therein, wherein the nonaqueous electrolyte comprises at least one compound selected from the group consisting of saturated chain hydrocarbons, saturated cyclic hydrocarbons and ethers having a fluorine atom, and further comprises at least one metal salt of at least one of a monofluorophosphate and a difluorophosphate,

wherein the at least one compound selected from the group consisting of saturated chain hydrocarbons, saturated cyclic hydrocarbons and ethers having a fluorine atom is contained in a total amount of 0.01-15% by mass based on the total mass of the nonaqueous electrolyte,

wherein the metal salt of the monofluorophosphate and/or difluorophosphate is contained in a total amount of from 0.001% by mass to 5% by mass based on the total mass of the nonaqueous electrolyte, and

wherein the saturated chain hydrocarbons have 5-20 carbon atoms, the saturated cyclic hydrocarbons have 3-20 carbon atoms, and the ethers having a fluorine atom are expressed by a general formula R 5 —O—R 6 , in which the R 5 is an alkyl group having 1-20 carbon atoms substituted with 1-30 fluorine atoms, and R 6 is an alkyl group which has 1-20 carbon atoms and may have be substituted with substituents.

2. The nonaqueous electrolyte according to claim 1 , wherein the at least one compound selected from the group consisting of saturated chain hydrocarbons, saturated cyclic hydrocarbons, aromatic compounds having a halogen atom, and ethers having a fluorine atom is at least one saturated cyclic hydrocarbon.

3. The nonaqueous electrolyte according to claim 1 , wherein the at least one compound selected from the group consisting of saturated chain hydrocarbons, saturated cyclic hydrocarbons, and ethers having a fluorine atom is ethers having a fluorine atom.

4. A nonaqueous-electrolyte secondary battery, comprising the nonaqueous electrolyte according to claim 1 , wherein the nonaqueous-electrolyte secondary battery including a negative electrode employing an active material comprising a carbonaceous material.

5. The nonaqueous electrolyte according to claim 1 , which is for use in a nonaqueous-electrolyte secondary battery including a negative electrode employing an active material having at least one kind of atom selected from the group consisting of aluminum atom, silicon atom, tin atom, lead atom, and titanium atom.

6. A nonaqueous-electrolyte secondary battery employing the nonaqueous electrolyte according to claim 1 .

7. The nonaqueous-electrolyte secondary battery according to claim 6 , wherein the battery comprises a positive electrode and/or a negative electrode which contains a metal salt of at least one of the monofluorophosphate and/or the difluorophosphate in the structure thereof.

8. A nonaqueous-electrolyte secondary battery comprising a negative electrode and a positive electrode which are capable of occluding/releasing lithium ions and a nonaqueous electrolyte, wherein the nonaqueous electrolyte is the nonaqueous electrolyte according to claim 1 .

9. The nonaqueous-electrolyte secondary battery according to claim 8 , wherein the negative electrode comprises a carbonaceous material.

10. The nonaqueous-electrolyte secondary battery according to claim 8 , wherein the negative electrode comprises a negative-electrode active material having at least one kind of atom selected from the group consisting of aluminum atom, silicon atom, tin atom, lead atom, and titanium atom.

11. The nonaqueous electrolyte according to claim 1 , wherein the metal salt of the monofluorophosphate and/or the difluorophosphate is a lithium salt.

12. The nonaqueous electrolyte according to claim 1 , wherein the monofluorophosphate and/or difluorophosphate is difluorophosphate.

13. The nonaqueous electrolyte according to claim 1 , which comprises at least one selected from the group consisting of heptane, cyclohexane and nonafluorobutyl ethyl ether in an amount of 0.3 to 10% by mass.

14. A nonaqueous-electrolyte secondary battery, comprising:

a negative electrode, a positive electrode and the nonaqueous electrolyte of claim 1 ,

wherein the negative electrode and the positive electrode are each capable of occluding/releasing lithium ions.

15. The battery of claim 14 , wherein the positive electrode comprises a mixture of a lithium-transition metal composite oxide, a binder and an organic conductive material.

16. The battery of claim 15 , wherein the negative electrode comprises a graphite powder.

17. A nonaqueous electrolyte, comprising:

a nonaqueous solvent, and

an electrolyte dissolved in the nonaqueous solvent;

wherein the nonaqueous electrolyte comprises at least one selected from the group consisting of a saturated chain hydrocarbon, a saturated cyclic hydrocarbon and an ether having a fluorine atom, and at least one metal salt of at least one selected from the group consisting of a monofluorophosphate and a difluorophosphate,

wherein the at least one compound selected from the group consisting of a saturated chain hydrocarbon, a saturated cyclic hydrocarbon and an ether having a fluorine atom is contained in a total amount of 0.01-15% by mass based on the total mass of the nonaqueous electrolyte,

wherein the metal salt of the monofluorophosphate and/or difluorophosphate is contained in a total amount of from 0.001% by mass to 5% by mass based on the total mass of the nonaqueous electrolyte, and

wherein the saturated chain hydrocarbons have 5-20 carbon atoms, the saturated cyclic hydrocarbons have 3-20 carbon atoms, and the ethers having a fluorine atom are expressed by a general formula R 5 —O—R 6 , in which the R 5 is an alkyl group having 1-20 carbon atoms substituted with 1-30 fluorine atoms, and R 6 is an alkyl group which has 1-20 carbon atoms and may have be substituted with substituents.

18. The nonaqueous electrolyte according to claim 17 , wherein the metal salt of the monofluorophosphate and/or the difluorophosphate is a lithium salt.

19. The nonaqueous electrolyte according to claim 17 , wherein the monofluorophosphate and/or difluorophosphate is difluorophosphate.